1. Field of the Invention
The present invention relates to an improved delivery system for delivering and deploying a medical device, such as a stent. More specifically, the invention relates to a delivery system for more accurate placement of a medical device such as a stent when using a pull back delivery system.
2. Description of the Related Art
Stents and delivery systems for deploying stents are highly developed and well known field of medical technology. Stents have many well known uses and applications. A stent is a prosthesis which is generally tubular and which is expanded radially in a vessel or lumen to maintain its patency. Stents are widely used in body vessels, body canals, ducts or other body lumens.
Stents, stent-grafts and the like are commonly delivered using a catheter delivery system. A common type of delivery system for delivering a self-expanding stent is called a pull back delivery system. This type of delivery system utilizes two catheters or shafts which are concentrically arranged, one around another. The stent is carried axially around the distal end of the inner catheter or shaft. The stent is carried to the delivery site on the distal end of the delivery device, held in its compressed delivery position by the outer shaft or catheter. Once at the desired placement site, the outer shaft is pulled back, releasing the stent to self-expand.
In testing, applicant's have observed that the portion of the catheter outside the body is typically not straight, but is curved during pull back. The frictional forces caused by pulling back the outer catheter or shaft cause the curve of the entire device to flatten out, which causes the distal end of the inner shaft or catheter to be urged forward. This undesired forward movement of the inner shaft often leads to inaccurate placement of the stent.
Another factor which can lead to placement inaccuracy are curves inside the body. A common and well known type of delivery is a contralateral insertion approach, where the distal end of the delivery device is placed on the opposite illiac from the original insertion site. In this case, the pull back delivery systems can also cause the curve placed inside the illiac vessels to straighten out or flatten slightly as the outer catheter or shaft is pulled back. This also causes undesired forward movement of the inner shaft, which can lead to inaccurate placement of the stent.
Schneider's WALLSTENT.RTM. product with Unistep.TM. delivery system utilizes a stainless steel tube as the inner shaft for the portion of the delivery system outside the body, and a plastic flexible tube as the inner shaft inside the body. The stainless steel tube prevents the proximal end of the device from curving outside the body. This device prevents placement error from the curve flattening out outside the body, but does not prevent placement error from a curve flattening out inside the body. Also, the Schneider approach may require different lengths of stainless steel tubing depending on the type of procedure, such as an ipsilateral femoral artery insertion versus a contralateral insertion, or a biliary duct insertion.
There remains a need in the art for a stent delivery system which prevents axial movement of one catheter shaft from causing forward movement of the other catheter shaft, which will allow for accurate placement of a medical device.